Paint PDF page backgrounds without navigation

internal/testutil/pdf_test.go

@@ -3,6 +3,7 @@ package testutil
 import (
 	"bytes"
 	"errors"
+	"fmt"
 	"image"
 	"image/color"
 	"image/png"
@@ -112,6 +113,102 @@ func TestInspectD2PDFKeepsSameTitleBoardsDistinct(t *testing.T) {
 	}
 }
 
+func TestPDFPageFillDoesNotDependOnNavigation(t *testing.T) {
+	for _, fill := range []struct {
+		name, value, operator, textOperator string
+	}{
+		{"dark", "#174ea6", "0.090 0.306 0.651 rg", "1.000 g"},
+		{"light", "#f2cf9b", "0.949 0.812 0.608 rg", "0.039 0.059 0.145 rg"},
+		{"empty", "", "1.000 g", "0.039 0.059 0.145 rg"},
+		{"transparent", "TrAnSpArEnT", "1.000 g", "0.039 0.059 0.145 rg"},
+	} {
+		for _, includeNav := range []bool{false, true} {
+			t.Run(fmt.Sprintf("%s/nav=%t", fill.name, includeNav), func(t *testing.T) {
+				t.Parallel()
+				// The tiny, partly transparent image leaves most of the page
+				// uncovered. Its own pixels cannot supply the page background.
+				pngBytes := pdfTestPNG(t)
+				document := pdf.Init()
+				parent := pdf.BoardTitle{Name: "Parent", BoardID: "root"}
+				child := pdf.BoardTitle{Name: "Child", BoardID: "root.layers.child"}
+				pageMap := map[string]int{parent.BoardID: 0, child.BoardID: 1}
+				for _, path := range [][]pdf.BoardTitle{{parent}, {parent, child}} {
+					if err := document.AddPDFPage(pngBytes, path, 0, fill.value, nil, 0, 0, 0, pageMap, includeNav); err != nil {
+						t.Fatal(err)
+					}
+				}
+				var output bytes.Buffer
+				if err := document.ExportTo(&output); err != nil {
+					t.Fatal(err)
+				}
+				inspection, err := InspectD2PDF(output.Bytes())
+				if err != nil {
+					t.Fatal(err)
+				}
+				if len(inspection.Pages) != 2 {
+					t.Fatalf("page count = %d, want 2", len(inspection.Pages))
+				}
+				if _, err := ComparePDFImages(output.Bytes(), [][]byte{pngBytes}, imagediff.Options{}); err != nil {
+					t.Fatal(err)
+				}
+				objects, err := splitPDFObjects(output.Bytes())
+				if err != nil {
+					t.Fatal(err)
+				}
+				byNumber := make(map[int]pdfObject, len(objects))
+				for _, object := range objects {
+					byNumber[object.number] = object
+				}
+				height := 576.0
+				if includeNav {
+					height += 72
+				}
+				for index, page := range inspection.Pages {
+					if page.Width != 576 || page.Height != height {
+						t.Fatalf("page %d dimensions = %.2fx%.2f, want 576x%.2f", index+1, page.Width, page.Height, height)
+					}
+					pageObject := byNumber[page.ObjectNumber]
+					contentNumber, err := pdfDictionaryInteger(pageObject.body, "Contents")
+					if err != nil {
+						t.Fatal(err)
+					}
+					content, err := decodePDFContentStream(byNumber[contentNumber])
+					if err != nil {
+						t.Fatal(err)
+					}
+					// Check the actual exported page stream, not the writer's
+					// remembered fill color. Paint the whole page once, below
+					// the image so transparent pixels reveal the selected fill.
+					rectangle := []byte(fmt.Sprintf("0.00 %.2f 576.00 -%.2f re f", height, height))
+					background := append([]byte(fill.operator+"\n"), rectangle...)
+					fillIndex := bytes.Index(content, background)
+					imageUse := pdfImageUseRE.FindIndex(content)
+					if fillIndex < 0 || bytes.Count(content, rectangle) != 1 || imageUse == nil || fillIndex >= imageUse[0] {
+						t.Fatalf("page %d must paint %q once before its image; stream:\n%s", index+1, background, content)
+					}
+					if includeNav {
+						if !bytes.Contains(content, []byte("\x00P\x00a\x00r\x00e\x00n\x00t")) ||
+							(index == 1 && !bytes.Contains(content, []byte("\x00C\x00h\x00i\x00l\x00d"))) {
+							t.Fatalf("page %d lost its navigation text", index+1)
+						}
+						if !bytes.Contains(content, []byte("q "+fill.textOperator+" BT")) {
+							t.Fatalf("page %d lost contrasting header text color %q", index+1, fill.textOperator)
+						}
+						if page.InternalLinks != index {
+							t.Fatalf("page %d internal links = %d, want %d", index+1, page.InternalLinks, index)
+						}
+						if index == 1 && !bytes.Contains(pageObject.body, []byte(fmt.Sprintf("/Dest [%d 0 R", inspection.Pages[0].ObjectNumber))) {
+							t.Fatal("child breadcrumb no longer targets the physical parent page")
+						}
+					} else if page.InternalLinks != 0 || bytes.Contains(content, []byte("Tj")) || bytes.Contains(content, []byte("TJ")) {
+						t.Fatalf("page %d gained a navigation header or link", index+1)
+					}
+				}
+			})
+		}
+	}
+}
+
 func pdfTestPNG(t *testing.T) []byte {
 	t.Helper()
 	img := image.NewNRGBA(image.Rect(0, 0, 3, 2))

lib/pdf/pdf.go

@@ -116,11 +116,11 @@ func (g *GoFPDF) AddPDFPage(png []byte, titlePath []BoardTitle, themeID int64, f
 
 	// Add page
 	g.pdf.AddPageFormat("", fpdf.SizeType{Wd: pageWidth, Ht: pageHeight + headerHeight})
+	g.pdf.SetFillColor(int(fillRGB.Red), int(fillRGB.Green), int(fillRGB.Blue))
+	g.pdf.Rect(0, 0, pageWidth, pageHeight+headerHeight, "F")
 
 	if includeNav {
 		// Draw header
-		g.pdf.SetFillColor(int(fillRGB.Red), int(fillRGB.Green), int(fillRGB.Blue))
-		g.pdf.Rect(0, 0, pageWidth, pageHeight+headerHeight, "F")
 		if fillRGB.IsLight() {
 			g.pdf.SetTextColor(10, 15, 37) // steel-900
 		} else {